Magnetic frequency reducer



Feb. 15, 1949. H, J, MCCREMQY 2,461,992

MAGNETIC FREQUENCY REDUCER Filed June 4, 1945 INVENTOR. HAROLD J. MOREARY ATTORNEY Patented Feb. 15, 1949 2,461,992 MAGNETIC FREQUENCYREDUCED Harold J. McCreary, Lombard, lll., assignor to AutomaticElectric Laboratories,

Inc., Chicago,

a corporation of Delaware Y Application June 4, 1945, Serial No. 597,46016 Claims. (Cl. 172-281) My invention relates in general to frequencyreducers which utilize saturation of a ferromagnetic core to producealternating currents having a frequency less than that of an alternatingcurrent driving source; and in particular toimprovements in theconstruction of the magnetic cores and in the arrangement of theelectrical circuits of such frequency reducers.

In my copending application, Serial No. 564, 879; filed November 23,1944 now Patent 2,445,857, issued July 27, 1948; I described a novelcore structure for use In this prior application my new core structurewas employed in a frequency changer arranged to produce an outputcurrent having a frequency which is an even harmonic or subharmonic ofthe frequency of an alternating current driving source. In the presentinvention I provide circuit arrangements for using this same corestructure to produce an output current which may have a frequency equalto an odd subharmonic of the frequency of the alternating currentdriving source, or which may have any other desired frequency less thanthat of the source. I accomplish this by inductively coupling aplurality of tuned circuits to the core, which is excited by a source ofalternating current in such a manner as to cause oscillating currents ofdifferent frequencies to flow in the tuned circuits, the sum of thefrequencies of the oscillating currents being equal to the frequency ofthe source.

The principal object of the present invention is to provide asubfrequency generator having a unitary magnetic structure.

Another object is to increase the efliciency of subfrequency generatorsthrough the use of an improved magnetic structure which permits one ormore windings to each wholly link several magnetic circuits in such amanner as to result in decreased copper losses and shorter, moreefficient, magnetic circuits than those previously used.

A further object of the invention is to provide a subfrequency generatorof the character described above wherein the plurality of tuned circuitsare inductively coupled to different magnetic' paths included in thecore and wherein these circuits are electrically connected so as tocontrol the wave-form of the oscillating current in the output circuitof the generator.

The invention has been illustrated in the form of schematic diagrams inthe accompanying drawing, in which:

Fig. 1 shows one form of my improved subfrequency generator;

in magnetic frequency changers.

Fig. 2 shows a modified form of the subfrequency generator shown in Fig.1;

Fig. 3 shows a further modified form of the subfrequency generator shownin Fig. 1;

Fig. 4 shows still another modification of the subfrequency generator;and

Figs. 1A through 4A show the waveforms of the output voltages obtainedfrom the corresponding modifications of the generator.

My invention comprises a saturable magnetic core constructed in the formof a cross with its extremities connected and having windings thereonsome of which are wound around the arms of the cross and others of whichare wound through diagonally opposite corners of the cross. Two or moreof these windings are serially connected to a source of alternatingcurrent, one or more windings are connected to a condenser and to anoutput circuit, and the remaining windings are connected to condensersand in some instances are interconnected with the first windings toproduce variations in the waveform of the output voltage.

Referring now to Fig. 1, there is shown a magnetic core I, which ispreferably constructed of laminations in the manner illustrated in theaforementioned copending application, upon which four windings arewound. One of these windings 2, is wound through one pair of diagonallyopposite corners of the intersection of the crossed members of the coreI. A second winding 3 is found through the remaining pair of diagonallyopposite corners of the intersection. Two other windings 4 and 5 areeach wound upon one of the arms of the cross formed in the center of thecore i. windings 2 and 3 are serially connected across a pair of inputterminals 6 and 1 which are in turn connected to a source of alternatingcurrent 8. Winding 3 is also connected to a pair of output terminals 9and III which are in turn connected to a load H. Condensers I2 and I3are connected across windings 2 and 3, respectively. Condenser I4 isconnected across winding 4 and this parallel combination is connected inseries with winding 5 and condenser IS. The core I has two magneticpaths included therein, one of these paths being directed through thevertical center leg, and the other path being directed through thehorizontal center leg. Winding 2 links these two paths so as to exertmagnetomotive forces therein which are directed upward in the verticalleg and to the left in the horizontal leg when. energized in onedirection. Winding 3 also links these two paths but in an opposite sensewith respect to winding 2 for winding 3 exerts magnetomotive forcestherein which are directed downward in the vertical leg and to the leftin the horizontal leg when energized in one direction. Thus it isapparent that the magnetomotive forces produced by currents flowing incoils 2 and 3 are always aiding in one of the paths and opposing in theother path. It has been found that alternating current having afrequencyequal to one third that of the source will be delivered to theload circuit with this arrangement when equal numbers of turns are usedon each coil and the condensers l2, l4, l5, and I3 bear ratios of1:4:l0z50, respectively. The waveform of the voltage developed acrossterminals 9 and I is shown in Fig. 1A.

Fig. 2 is identical to Fig. 1 excepting that in this case winding 3 isalso connected in series with winding 5. condenser l5, and the parallelcombination of winding 4 and condenser l4. change in connections bringsabout a considerable change in the waveform of the output voltagedeveloped across terminals 9 and 10, as shown in Fig. 2A. In this casethe output'contains a large component of the input frequency, whichcomponent is negligible in the circuit of Fig. 1.

In Fig. 3 the connections have been further altered by connectingcondenser l4 across the series combination of winding 5 and condenser inplace of across winding 4. The waveform of the output voltage developedacross terminals 9 and Ill with these connections is shown in Fig. 3A..This is seen to be nearly a square wave which may advantageously beused as a source of impulses by rectification, or by inserting a sourceof direct current in series with the output, so as to provide aunidirectional pulsating output voltage. The steep wavefront and sharpcorners in this wave indicate the presence of numerous high orderharmonics, which are desirable in a subfrequency generator which is usedas a source of ringing current in a telephone system. In such a system,the ringing current must contain high.

order harmonics in order to produce a satisfactory ring-back signalsince the fundamental frequency of the ringing current is too low to beefficiently transmitted over the circuits involved and reproduced by thecalling partys receiver.

The circuit arrangements described so far are particularly suited to theproduction of an alternating current having a frequency equal toonethird that of the source. The modification illustrated in Fig. 4 isreadily adapted to produce an alternatin current having any desiredfrequency less than that of the source. In this arrangement twoadditional windings, f6 and I1, each wound on one arm of the crossformed in 'the center of the core I l, are connected in series withwinding 2 across the input terminals 6 and I. The output current isobtained from windings 4 and 5, which are serially connected to outputterminals 9 and iii across which condenser 18 is connected to tune theoutput branch to the output frequency. Winding 3 is in this case dividedinto two parts 3a and 3b. One of these parts 3a is tuned by condenser l3to a frequency equa to that of the source 8 less the desired outputfrequency, and the other part 312 is connected to a source of directcurrent 19 in series with a choke coil 20 and an adjustable resistor 2|.The choke coil 20 is used to prevent alternating current from flowingthrough battery H! as a result of the alternating voltages induced inwinding 31). Resistor 2! is used to control the magnitude of the directcurrent flowing through winding 3b so as to bias This the core H to adesired portion of its magnetization current to thereby facilitate thestarting of oscillations in the tuned circuits. The wave-form of theoutput voltage developed across terminals 9 and Ill, when condensers l3and I8 are chosen so as to make the output frequency equal to one thirdthat of the source 8, is shown in Fig. 4A.

In all of the previously disclosed subfrequency .generators employing aplurality of tuned circuits coupled by a saturable magnetic core meansit has been necessary to employ linear inductances andcondensers in eachtuned circuit. I have found that the use of separate linear inductancesin each tuned circuit is unnecessary when the several tuned circuitsinclude windings linking different magnetic paths in the saturable coreas herein illustrated, since in this case each winding may act as alinear inductance during the intervals when the particular magnetic pathto which it is coupled is not saturated.

I have therefore been able to produce a subfrequency generator with aunitary magnetic structure,

struction. By electrically coupling in various ways the several tunedcircuits, each of which is .inductively coupled to a different magneticflux path in a common core, I am able to control the waveform of theoutput voltage of my subfrequency generator.

Although I have described my invention with a certain degree ofparticularity, it should be understood that the present disclosure hasbeen I made only by way of example and that numerous changes in thedetails of construction and the combination and arrangement of parts maybe resorted to without departing from the spirit and scope of theinvention as hereinafter claimed.

What is claimed is:

1. A subfrequency generator comprising a saturable magnetic core means,a source of alternating current, a primary circuit including a windingon said core means connected to said source, a secondary circuitincluding a winding on said core means connected to a load circuit, anauxiliary circuit including a winding on said core means, condensersconnected in said secondary and auxiliary circuits tuning them todifferent frequencles such that the sum thereof is equal to thefrequency of said source, said secondary and auxiliary circuits beingdevoid of inductance elements other than the ,windings on said coremeans, the excitation of said core means by said source causingoscillating currents to be produced in said secondary and auxiliarycircuits of frequencies corresponding to the tuning thereof.

2. A subfrequency generator comprising a saturable magnetic core means,a source of alternating current, a primary circuit including a windingon said core means connected to said source, a secondary circuitincluding a winding on said core means connected to a load, an auxiliarycircuit including a winding on said core means, condensers connected insaid circuits tuning them to different frequencies such that the sumthereof is equal to the frequency of said source, the windings on saidcore means constituting the sole inductance elements in said circuits,the excitation of said core means by said source causing oscillatingcurrents to be produced in said circuits of frequencies corresponding tothe tuning thereof.

3. In a subfrequency generator, a saturable magnetic core having twomagnetic flux paths, a first single section winding on said core linkingsaid paths in one sense, a second single section winding on said corelinking said paths in an opposite sense, a source of alternatingcurrent, a primary circuit including one of said windings connected tosaid source, a secondary circuit including the other of said windingsconnected to a load, an auxiliary circuit including windings on saidcore each linking only one of said paths, condensers connected in saidcircuits so as to form a plurality of oscillatory circuits, theexcitation of said core by said source causing oscillating currents toflow in said oscillatory circuits of frequencies such that the sumthereof is equal to the frequency of said source.

4. In a subfrequency generator, a saturable magnetic core having twomagnetic paths, a first single section winding on said core linking saidpaths in one sense, a second single section winding on said core linkingsaid paths in an opposite sense, a source of alternating current, aprimary circuit including one of said windings connected to said source,an auxiliary circuit including the other of said windings, a secondarycircuit including windings on said core each linking only one of saidpaths, condensers connected in certain of said circuits so as to form aplurality of oscillatory circuits, the excitation of said core by saidsource causing oscillating currents to flow in said oscillatory circuitsof frequencies such that the sum thereof is equal. to the frequency ofsaid source.

5. A subfrequency generator comprising a saturable magnetic coreconstructed in the form of a cross with its extremities connected, afirst coil wound through one pair of diagonally opposite corners of thecross, a second coil wound through the remaining pair of diagonallyopposite corners of the cross, a third and a fourth coil each wound onone of the arms of the cross, a source of alternating current connectedto one' of said windings, condensers connected to the other windings soas to form a plurality of oscillatory circuits, a load connected to oneof said oscillatory circuits, the excitation of said core by said sourcecausing oscillating currents to flow in said circuits of frequenciessuch that the sum thereof is equal to the frequency of said source.

6. A subfrequency generator comprising a saturable magnetic coreconstructed in the form of a cross with its extremities connected, aplurality of windings linking different flux paths of said core, asource of alternating current connected to one of said windings,condensers connected to said windings so as to form a plurality ofoscillatory circuits, a load connected to one of said oscillatorycircuits, the excitation of said core by said source causing oscillatingcurrents to flow in said circuits of frequencies such that the sumthereof is equal to the frequency of said source.

'7. A subfrequency generator comprising a saturable magnetic core means,a source of alternating current, a primary circuit including a windingon said core means connected to said source, a secondary circuitincluding a winding on said core means connected to a load, an auxiliarycircuit including a winding on said 6 condensers connected in saidcirthem to different frequencies such that the sum thereof is equal tothe frequency of said source, certain of said circuits beingelectrically connected to eflect an interchange of energy therebetweenso as to control the waveform of the reduced frequency alternatingcurrent delivered to the load.

8. A subfrequency generator comprising a saturable magnetic core and apair of single section windings thereon, said core having two flux pathswhich link the senses, a primary circuit including one of said windingsand a source of alternating current, a

core means, cuits to tune secondary circuit including the other ofsaidwindings and a load, further windings on said core, and condensersassociated with said further windings and with said secondary circuit tocause alternating current having a frequency less than that of saidsource to be delivered to the load.

9. A subfrequency generator comprising a saturable magnetic core and apair of single section windings thereon, said core having two flux pathswhich link the pair of windings in opposite senses, a primary circuitincluding one of said windings and a source of alternating current,further windings on said core, a secondary circuit including saidfurther windings and a load, and condensers associated with the other ofsaid first windings and with said secondary circuit to cause alternatingcurrent having a frequency less than that of said source to be deliveredto the load.

10. A subfrequency generator comprising a saturable magnetic core, aprimary circuit including a source of alternating current and a firstwinding on said core, a secondary circuit including a load and a secondwinding on said core, an auxiliary circuit including a third winding onsaid core, said core having two flux paths which link the whole of twoof said windings in opposite senses, and condensers associated with saidauxiliary circuit and said secondary circuit to cause subfrequencyalternating currents to be delivered to the load.

11. In a static frequency changer, a saturable magnetic core having fouropenings therein, a first coil wound through one diagonally oppositepair of said openings, a second coil wound through the other diagonallyopposite pair of said openings, a third coil wound through an adjacentpair of said openings, a source of alternating current connected to oneof said coils, a condenser and a load connected to another of saidcoils, and a further condenser connected to the remaining coil, wherebyalternating current having a frequency less than that of said source isdelivered to said load.

12. In a static frequency changer, a saturable magnetic core having atleast four openings therein, a first coil wound through one diagonallyopposite pair of said openings, a second coil wound through anotherdiagonally opposite pair of said openings, a third coil wound through anadjacent pair of said openings, a source of alternating currentconnected to one of said coils, a condenser and a load connected toanother of said coils, and a further condenser connected to theremaining coil, whereby alternating current having a frequency less isdelivered to said load.

13. In a static frequency changer, a saturable magnetic core having fouropenings therein, a first coil wound through one diagonally oppositepair of said openings, a second coil wound pair of windings inoppositethan that of said source openings, one of said openings beingcommon to said third and fourth coils.

15. In a static frequency changer, a saturable magnetic core having fouropenings therein, a first coil wound through one diagonally oppositepair of said openings, a second coil wound through the other diagonallyopposite pair of said openings, and four further coils each woundthrough a difierent adjacent pair of said openings.

16. In a static frequency changer, a saturable magnetic core having aplurality of diagonally opposed openings therein, a plurality of coilseach wound through a diagonally opposed pair of said openings, and aplurality of further coils each wound through an adjacent pair of saidopenings.

HAROLD J. McCREARY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,088,620 Stacker Aug. 3, 19372,179,386 Stocker Nov. '7, 1939 FOREIGN PATENTS Number Country Date448,341 Great Britain June 5, 1936

